Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art.
Hydrogels have emerged as leading candidates for various tissue engineering applications due to their similarity with the native extracellular matrix (ECM, Peppas et al. (2006)). Among the natural hydrogels, elastin-based biomaterials have shown remarkable properties including elasticity, self-assembly, long-term stability, and biological activity.
Various cross-linking approaches have been used to produce three-dimensional elastin-based hydrogels from recombinant human tropoelastin, α-elastin, and engineered elastin-like polypeptides (Mithieux et al. (2004) and Annabi et al. (2010)). The resultant hydrogels have shown biocompatibility and supported cell growth both in vitro and in vivo. However, non-homogenous cell distribution within the three-dimensional structures of these hydrogels has been an issue (Mithieux et al. (2004)). This has generally arisen from the fact that in a pre-formed gel (i.e. a gel that has been prepared before addition of cells to it) cell distribution is generally a function of cell growth or spreading throughout the gel. Put in other words, distribution of cells throughout a pre-formed gel arises as the cells replicate or move throughout the hydrogel. One problem is that once seeded in a pre-formed gel, many cells have limited capacity for movement, or require significant time to generate sufficient cell number for complete distribution through and complete colonisation of a gel. The end result may be clumping of cells and formation of cell colonies in localised regions of the gel where the cells have been seeded, rather than dispersion or distribution of cells throughout a hydrogel.
It has not been possible to incorporate cells in or on a hydrogel during hydrogel formation. This is because harsh conditions used in the fabrication techniques, such as the use of chemical cross-linkers (Mithieux et al. (2004)), organic solvents (Annabi et al. (2009)) and high pressure (Annabi et al. (2010) and Annabi et al. (2009)), have prevented the possibility of cell incorporation during hydrogel formation. In particular, previous methods have prevented the incorporation of cells evenly in the matrix without damaging cell viability
Many applications of hydrogels require the hydrogel to maintain a particular shape or pattern so as to provide the desired end function. For example, it may be necessary for the hydrogel to provide grooves or other cell guiding structures for aligning cells in a desired direction. One problem with many hydrogels is that the shapes or patterns formed on them tend not to persist for sufficient periods of time required for the cells to adopt the required alignment.
In nearly all applications, hydrogels are required to support cell proliferation and spreading. However, many hydrogels limit the capacity for either or both of these cell activities. One further problem of some hydrogels is that they have a structural characteristic that impedes the desired functional characteristic of the particular cell of interest. For example, the hydrogel may have a degree of elasticity which is incompatible with a desired cell contraction, and which therefore masks the desired cell property.
There is therefore a need to develop hydrogels, scaffolds and the like that can be used in tissue engineering applications. Ideally, these scaffolds should be biocompatible (i.e. non-toxic to biological tissue and non-immunogenic), durable, stable, have the desired mechanical properties (for example, strength and elasticity) and allow for the provision of viable cells that are, preferably, distributed more or less evenly throughout and upon the hydrogel, or otherwise distributed in a desired or pre-selected or pre-defined pattern in or on the hydrogel.